The present invention relates to prosthetic vascular grafts and, more particularly, to a vascular graft for a primary vessel adapted to bridge a side branch, especially for providing a support tube for a primary graft located in the primary vessel on one side of the side branch.
An aneurysm is a ballooning of the wall of an artery resulting from weakening due to disease or other condition. Left untreated, the aneurysm may rupture, resulting in severe loss of blood and potentially death. An aneurysm in the abdominal aorta is the most common form of arterial aneurysm. The abdominal aorta connects the ascending aorta at the heart to the circulatory system of the trunk and lower body. The abdominal aorta extends downward from the heart in front of and parallel to the spine, through the thorax and abdomen, and branches off in a plurality of side vessels. Among other branching vessels, the abdominal aorta supplies the two kidneys via oppositely-directed renal arteries. Below the renal arteries, the abdominal aorta continues to about the level of the fourth lumbar vertebrae and divides at a Y-junction into the left and right iliac arteries, which supply blood to the lower extremities.
A common location for an aortic aneurysm is in the section of aorta between the renal and iliac arteries. Without rapid surgical intervention, a rupture of the abdominal aorta is commonly fatal because of the high volume of blood flow within the aorta. Conventional surgical intervention involves penetrating the abdominal wall to the location of the aneurysm to reinforce or replace the diseased section of the aorta. Typically, a prosthetic tube graft replaces the area of, or proximal and distal zones abutting, a potential rupture portion of the aorta. Unfortunately, conventional surgical intervention has resulted in substantial morbidity rates, and at the very least a protracted recovery period. Likewise, cost and other constraints militate for a longstanding need for endovascular intervention.
In recent years, methods and devices have been developed to treat an aortic aneurysm without opening up the abdominal wall. These new techniques typically involve a catheter-carried tubular graft delivered upward from the femoral artery through the iliac artery and into the region of the aneurysm. The graft normally includes a tubular graft body supported by an expandable stent, either self-expanding or balloon-expanding. The balloon-expanding type of stent naturally requires an expansion balloon, while the self-expanding type is simply deployed from the end of a tubular sheath. Implacement issues impact upon both known techniques.
If the aneurysm affects the Y-junction between the abdominal aorta and the iliac arteries, a bifurcated graft is typically used. A trunk portion of the bifurcated graft is secured to a healthy section of the abdominal aorta just below the renal arteries, and branched legs of the graft are secured within each of the iliac arteries, sometimes via a tubular extension graft. This procedure does not involve cardiopulmonary bypass, and thus blood continues to flow downward through the abdominal aorta. Certain complications arise in anchoring the graft to the inner wall of the vessel, because of the high blood flow both during the procedure and afterward. Indeed, the risk of grafts migrating within a vessel is a problem in many locations, not just in the abdominal aorta. In addition, the abdominal aorta may be aneurysmic very close to the renal arteries, which results in a fairly poor substrate within which to secure a repair graft. In fact, surgeons require various minimum lengths of healthy aortic wall below the renal arteries before an endovascular graft repair is indicated, or else a conventional invasive technique must be used. Moreover, the same consideration of a minimum healthy portion of the host vessel applies in other areas, especially with regard to the portion of the aorta adjacent the branching subclavian or carotid arteries.
A number of techniques have been proposed for anchoring grafts to vessel walls, most notably the use of barbs or hooks extending outward from graft that embed themselves into the vessel wall. Although these devices secure the graft, they may damage the vessel wall and cause complications. Alternatively, portions of the stent may extend beyond the upstream end of the graft body and be bent outward into contact with the vessel wall, either from a pre- or shape memory-bias, or from expansion of a balloon in this region.
In the context of repairing an aneurysm in the abdominal aorta, some manufacturers have provided a stent at the upper end of a bifurcated graft that extends across the renal arteries. For example, the TALENT brand of Endovascular Stent-Graft System available from World Medical of Sunrise, Florida, includes an undulating wire support frame extending above the graft body intended for supra-renal fixation. Likewise, the ZENITH AAA brand of Endovascular Graft from Cook, Inc. of Bloomington, Indiana, utilizes an undulating wire support having barbs for supra-renal fixation of the graft. However, because these wires extend across the opening of the branching renal arteries they present a certain impediment to blood flow therethrough. Moreover, any structure placed in the path of blood flow may tend to initiate the blood clotting cascade, which in turn, may generate free-floating emboli that would adversely impact the kidneys, or other organ that is perfused through the affected side branch. Because the kidneys are highly susceptible to injury from incursion of such emboli, it is highly desirable to avoid even the possibility of blood clotting at the mouth of the renal arteries.
Despite much work in this highly competitive field, there is still a need for a more secure means of anchoring a bifurcated graft in the abdominal aorta. More generally, there is a need for a more secure means of anchoring a tubular graft in a primary vessel in the vicinity of a vessel side branch.
The present invention comprises a vascular graft adapted for placement in a primary blood vessel and suited to bridge a vessel side branch. The graft comprises a tubular structure defining an outer surface, a first portion of the outer surface being sized to contact and support the blood vessel on one side of the side branch, and a second portion of the outer surface being sized to contact and support the blood vessel on the other side of the side branch. The tubular structure defines an aperture for alignment with the side branch so as to permit blood flow between the blood vessel and the side branch. The first and second portions may be separated across a gap and the graft further may include at least one bridging member traversing the gap and connecting the first and second portions so as to prevent relative axial separation of the two portions after implantation, the aperture being defined between the bridging member and the first and second portions. There are desirably at least two bridging members and two apertures, and potentially four bridging members and four apertures. Further, the bridging member may be a relatively rigid strut.
In another aspect, the invention provides a vascular graft adapted for placement in a primary blood vessel and suited to bridge a vessel side branch, comprising:
a first tubular structure sized to contact and support the blood vessel on one side of the side branch;
a second tubular structure sized to contact and support the blood vessel on the other side of the side branch; and
at least one bridging member connecting the first and second tubular structures so as to define an aperture in the vascular graft sized for blood to flow through between the blood vessel and the side branch.
At least one of the first and second tubular structures desirably comprises a flexible graft body and a support stent, wherein the strut is directly connected to the graft body. More preferably, the flexible graft body is only provided in one of the first or second tubular structures, the other tubular structure being defined solely by the stent.
In a further aspect, the invention provides a vascular graft system adapted for placement in a primary blood vessel and adjacent a vessel side branch. The system includes a tubular support graft including a first tubular structure sized to contact and support the blood vessel on one side of the side branch, and a second tubular structure spaced from and connected to the first tubular structure and sized to contact and support the blood vessel on the other side of the side branch. The system further includes a tubular primary graft sized to co-axially couple with the first tubular structure. At least one bridging member may connect the first and second tubular structures so as to prevent relative axial separation of the two tubular structures after implantation, an aperture being defined between the bridging member and the first and second tubular structures of a sufficient size to permit blood flow though the vessel side branch. In one application of the system, the primary vessel is the abdominal aorta, the vessel side branch comprises the renal arteries, and the tubular primary graft is a portion of a bifurcated graft. In addition, at least one of the first and second tubular structures preferably comprises a flexible graft body and a support stent, and more preferably the flexible graft body is only provided in the tubular structure that is disposed infra-renally, the other tubular structure disposed supra-renally being defined solely by the stent. The stent may be self-expandable or balloon-expandable.
Methods of supporting a tubular primary graft in a primary blood vessel adjacent a vessel side branch is also provide by the present invention. One method includes,
providing a tubular support graft including a first tubular section and a second tubular section connected to the first tubular section;
delivering the tubular support graft into an implant position;
deploying the tubular support graft so that the first tubular section contacts and supports the blood vessel on one side of the side branch and the second tubular section contacts and supports the blood vessel on the other side of the side branch;
providing a tubular primary graft having a first end;
delivering the first end of the primary graft within the support graft second tubular section; and
radially expanding the first end of the primary graft against the inner surface of the second tubular section.
Another method includes the steps of:
providing a tubular primary graft having a first end;
delivering the first end of the primary graft into an implant position; and
radially expanding the first end of the primary graft against the inner surface of the blood vessel on one side of the side branch.
providing a tubular support graft including a first tubular section and a second tubular section connected to the first tubular section;
delivering the tubular support graft so that the second tubular section is within the primary graft first end; and
radially expanding the tubular support graft so that the first tubular section contacts and supports the blood vessel on one side of the side branch and the second tubular section contacts and supports the inner surface of the primary graft first end.
Either method is preferably accomplished by endoluminally delivering both the tubular support graft and the tubular primary graft.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.